Cardiorespiratory and metabolic characteristics of detraining in humans

Detraining can be defined as the partial or complete loss of training-induced adaptations, in response to an insufficient training stimulus. Detraining is characterized, among other changes, by marked alterations in the cardiorespiratory system and the metabolic patterns during exercise. In highly trained athletes, insufficient training induces a rapid decline in VO2max, but it remains above control values. Exercise heart rate increases insufficiently to counterbalance the decreased stroke volume resulting from a rapid blood volume loss, and maximal cardiac output is thus reduced. Cardiac dimensions are also reduced, as well as ventilatory efficiency. Consequently, endurance performance is also markedly impaired. These changes are more moderate in recently trained subjects in the short-term, but recently acquired VO2max gains are completely lost after training stoppage periods longer than 4 wk. From a metabolic viewpoint, even short-term inactivity implies an increased reliance on carbohydrate metabolism during exercise, as shown by a higher exercise respiratory exchange ratio. This may result from a reduced insulin sensitivity and GLUT-4 transporter protein content, coupled with a lowered muscle lipoprotein lipase activity. These metabolic changes may take place within 10 d of training cessation. Resting muscle glycogen concentration returns to baseline within a few weeks without training, and trained athletes' lactate threshold is also lowered, but still remains above untrained values.     

Detraining: loss of training-induced physiological and performance adaptations. Part II: Long term insufficient training stimulus

This part II discusses detraining following an insufficient training stimulus period longer than 4 weeks, as well as several strategies that may be useful to avoid its negative impact. The maximal oxygen uptake (VO2max) of athletes declines markedly but remains above control values during long term detraining, whereas recently acquired VO2max gains are completely lost. This is partly due to reduced blood volume, cardiac dimensions and ventilatory efficiency, resulting in lower stroke volume and cardiac output, despite increased heart rates. Endurance performance is accordingly impaired. Resting muscle glycogen levels return to baseline, carbohydrate utilisation increases and the lactate threshold is lowered, although it remains above untrained values in the highly trained. At the muscle level, capillarisation, arterial-venous oxygen difference and oxidative enzyme activities decline in athletes and are completely reversed in recently trained individuals, contributing significantly to the long term loss in VO2max. Oxidative fibre proportion is decreased in endurance athletes, whereas it increases in strength athletes, whose fibre areas are significantly reduced. Force production declines slowly, and usually remains above control values for very long periods. All these negative effects can be avoided or limited by reduced training strategies, as long as training intensity is maintained and frequency reduced only moderately. On the other hand, training volume can be markedly reduced. Cross-training may also be effective in maintaining training-induced adaptations. Athletes should use similar-mode exercise, but moderately trained individuals could also benefit from dissimilar-mode cross-training. Finally, the existence of a cross-transfer effect between ipsilateral and contralateral limbs should be considered in order to limit detraining during periods of unilateral immobilisation.     

Detraining: loss of training-induced physiological and performance adaptations. Part I: short term insufficient training stimulus

Detraining is the partial or complete loss of training-induced adaptations, in response to an insufficient training stimulus. Detraining characteristics may be different depending on the duration of training cessation or insufficient training. Short term detraining (less than 4 weeks of insufficient training stimulus) is analysed in part I of this review, whereas part II will deal with long term detraining (more than 4 weeks of insufficient training stimulus). Short term cardiorespiratory detraining is characterised in highly trained athletes by a rapid decline in maximal oxygen uptake (VO2max) and blood volume. Exercise heart rate increases insufficiently to counterbalance the decreased stroke volume, and maximal cardiac output is thus reduced. Ventilatory efficiency and endurance performance are also impaired. These changes are more moderate in recently trained individuals. From a metabolic viewpoint, short term inactivity implies an increased reliance on carbohydrate metabolism during exercise, as shown by a higher exercise respiratory exchange ratio, and lowered lipase activity, GLUT-4 content, glycogen level and lactate threshold. At the muscle level, capillary density and oxidative enzyme activities are reduced. Training-induced changes in fibre cross-sectional area are reversed, but strength performance declines are limited. Hormonal changes include a reduced insulin sensitivity, a possible increase in testosterone and growth hormone levels in strength athletes, and a reversal of short term training-induced adaptations in fluid-electrolyte regulating hormones.     

The scientific basis for high-intensity interval training: optimising training programmes and maximising performance in highly trained endurance athletes.

While the physiological adaptations that occur following endurance training in previously sedentary and recreationally active individuals are relatively well understood, the adaptations to training in already highly trained endurance athletes remain unclear. While significant improvements in endurance performance and corresponding physiological markers are evident following submaximal endurance training in sedentary and recreationally active groups, an additional increase in submaximal training (i.e. volume) in highly trained individuals does not appear to further enhance either endurance performance or associated physiological variables [e.g. peak oxygen uptake (VO2peak), oxidative enzyme activity]. It seems that, for athletes who are already trained, improvements in endurance performance can be achieved only through high-intensity interval training (HIT). The limited research which has examined changes in muscle enzyme activity in highly trained athletes, following HIT, has revealed no change in oxidative or glycolytic enzyme activity, despite significant improvements in endurance performance (p < 0.05). Instead, an increase in skeletal muscle buffering capacity may be one mechanism responsible for an improvement in endurance performance. Changes in plasma volume, stroke volume, as well as muscle cation pumps, myoglobin, capillary density and fibre type characteristics have yet to be investigated in response to HIT with the highly trained athlete. Information relating to HIT programme optimisation in endurance athletes is also very sparse. Preliminary work using the velocity at which VO2max is achieved (V(max)) as the interval intensity, and fractions (50 to 75%) of the time to exhaustion at V(max) (T(max)) as the interval duration has been successful in eliciting improvements in performance in long-distance runners. However, V(max) and T(max) have not been used with cyclists. Instead, HIT programme optimisation research in cyclists has revealed that repeated supramaximal sprinting may be equally effective as more traditional HIT programmes for eliciting improvements in endurance performance. Further examination of the biochemical and physiological adaptations which accompany different HIT programmes, as well as investigation into the optimal HIT programme for eliciting performance enhancements in highly trained athletes is required.     

The influence of direct supervision of resistance training on strength performance

PURPOSE: The purpose of this study was to compare changes in maximal strength, power, and muscular endurance after 12 wk of periodized heavy-resistance training directly supervised by a personal trainer (SUP) versus unsupervised training (UNSUP). METHODS: Twenty moderately trained men aged 24.6 +/- 1.0 yr (mean +/- SE) were randomly assigned to either the SUP group (N = 10) or the UNSUP group (N = 8). Both groups performed identical linear periodized resistance training programs consisting of preparatory (10-12 repetitions maximum (RM)), hypertrophy (8 to 10-RM), strength (5 to 8-RM), and peaking phases (3 to 6-RM) using free-weight and variable-resistance machine exercises. Subjects were tested for maximal squat and bench press strength (1-RM), squat jump power output, bench press muscular endurance, and body composition at week 0 and after 12 wk of training. RESULTS: Mean training loads (kg per set) per week were significantly (P < 0.05) greater in the SUP group than the UNSUP group at weeks 7 through 11 for the squat, and weeks 3 and 7 through 12 for the bench press exercises. The rates of increase (slope) of squat and bench press kg per set were significantly greater in the SUP group. Maximal squat and bench press strength were significantly greater at week 12 in the SUP group. Squat and bench press 1-RM, and mean and peak power output increased significantly after training in both groups. Relative local muscular endurance (80% of 1-RM) was not compromised in either group despite significantly greater loads utilized in bench press muscular endurance testing after training. Body mass, fat mass, and fat-free mass increased significantly after training in the SUP group. CONCLUSION: Directly supervised, heavy-resistance training in moderately trained men resulted in a greater rate of training load increase and magnitude which resulted in greater maximal strength gains compared with unsupervised training.     

Cardiac size and VO2max do not decrease after short-term exercise cessation

We measured maximum oxygen uptake, estimated changes in plasma volume, and the cardiac dimensions of 15 male competitive distance runners (28.2 +/- 5.6 yr of age, mean +/- SD) before and after 10 days of exercise cessation. Subjects were habitually active but adjusted their training to run 16 km daily for 2 wk before the study. Subjects were maintained on defined diets for the week before and during the detraining period. Average body weight decreased 1.0 +/- 0.5 kg (P less than 0.001) within 2 days of exercise cessation and was accompanied by a 5.0 +/- 5.9% (P less than 0.01) decrease in estimated plasma volume. No additional changes in body weight and plasma volume occurred during the study, and estimated percent body fat did not change. Resting heart rate, blood pressure, and cardiac dimensions were also unchanged with physical inactivity. In addition, maximum oxygen uptake was not altered although peak exercise heart rate was an average of 9 +/- 5 beats X min-1 (P less than 0.01) or 5% higher after detraining. We conclude that short periods of exercise cessation decrease estimated plasma volume and increase the maximum exercise heart rate of endurance athletes but do not alter their cardiac dimensions or maximum oxygen uptake.     

The effect of detraining and reduced training on the physiological adaptations to aerobic exercise training

In previously sedentary individuals, regularly performed aerobic exercise results in significant improvements in exercise capacity. The development of peak exercise performance, as typified by competitive endurance athletes, is dependent upon several months to years of aerobic training. The physiological adaptations associated with these improvements in both maximal exercise performance, as reflected by increases in maximal oxygen uptake (VO2max), and submaximal exercise endurance include increases in both cardiovascular function and skeletal muscle oxidative capacity. Despite prolonged periods of aerobic training, reductions in maximal and submaximal exercise performance occur within weeks after the cessation of training. These losses in exercise performance coincide with declines in cardiovascular function and muscle metabolic potential. Significant reductions in VO2max have been reported to occur within 2 to 4 weeks of detraining. This initial rapid decline in VO2max is likely related to a corresponding fall in maximal cardiac output which, in turn, appears to be mediated by a reduced stroke volume with little or no change in maximal heart rate. A loss in blood volume appears to, at least partially, account for the decline in stroke volume and VO2max during the initial weeks of detraining, although changes in cardiac hypertrophy, total haemoglobin content, skeletal muscle capillarisation and temperature regulation have been suggested as possible mediating factors. When detraining continues beyond 2 to 4 weeks, further declines in VO2max appear to be a function of corresponding reductions in maximal arterial-venous (mixed) oxygen difference. Whether reductions in oxygen delivery to and/or extraction by working muscle regulates this progressive decline is not readily apparent. Changes in maximal oxygen delivery may result from decreases in total haemoglobin content and/or maximal muscle blood flow and vascular conductance. The declines in skeletal muscle oxidative enzyme activity observed with detraining are not causally linked to changes in VO2max but appear to be functionally related to the accelerated carbohydrate oxidation and lactate production observed during exercise at a given intensity. Alternatively, reductions in submaximal exercise performance may be related to changes in the mean transit time of blood flow through the active muscle and/or the thermoregulatory response (i.e. degree of thermal strain) to exercise. In contrast to the responses observed with detraining, currently available research indicates that the adaptations to aerobic training may be retained for at least several months when training is maintained at a reduced level. Reductions of one- to two-thirds in training frequency and/or duration do not significantly alter VO2max or submaximal endurance time provided the intensity of each exercise session is maintained.(ABSTRACT TRUNCATED AT 400 WORDS)     

Physiological Characteristics of Major League Baseball Players

Performance characteristics of professional athletes are of interest to those involved in sports. Major league baseball players were tested for muscular strength, cardiovascular endurance, and body composition. Comparisons were made among positions and with other professional athletes. Results indicated that differences in strength and body composition existed among positions. Cardiovascular endurance of baseball players was comparable to that reported for other professional athletes. These data may be useful as a point of reference for coaching, testing, training, and selecting athletes.     

Cross transfer effects of muscular endurance during training and detraining

BACKGROUND: To clarify 1) how the cross-transfer effect, obtained in a contralateral untrained forearm through a 4-week ipsilateral endurance training regimen, is changed during detraining; and 2) how blood flow to the untrained limb is related to the transfer effect of muscular endurance during training and detraining periods. METHODS: Training regimen: hand-grip training by means of a hand-ergometer with a work-load of 1/3 of the maximum handgrip strength 5 times a week for 4 weeks. Blood flow: a mercury-in-rubber strain-gauge for venous occlusion plethysmography. Measures: 1) maximal number of contractions to determine the muscular endurance; 2) reactive hyperaemic blood flow response (RHBF3) to determine whether maximal vasodilatory capacity would be changed in both the forearms post-training and detraining; and 3) maximal work-related blood flow. RESULTS: We found significant increments both in the muscle endurance and the maximal work-related blood flow not only in the trained (+125%, +30%) but also in the untrained (+40%, +19%) forearms. During detraining, we found decreases both in the muscle endurance and the maximal work-related blood flow (-22%, p<0.01; -16%, p=0.053) of the trained forearm. However, in the untrained arm (-3%, NS) the cross-transfer effect of muscular endurance remained unchanged despite a drop in the maximal work-related blood flow (-17%, p<0.05). The RHBF3 did not change in either of the forearms during the whole periods. CONCLUSIONS: These findings suggest that the maintenance of the cross transfer effect of muscle endurance during detraining cannot be explained on the basis of changes in forearm blood flow.     

Intermittent hypoxia improves endurance performance and submaximal exercise efficiency

The purpose of the present study was to elucidate the influence of intermittent hypobaric hypoxia at rest on endurance performance and cardiorespiratory and hematological adaptations in trained endurance athletes. Twelve trained male endurance runners were assigned to either a hypoxic group (n = 6) or a control group (n = 6). The subjects in the hypoxic group were exposed to a simulated altitude of 4500 m for 90 min, three times a week for 3 weeks. The measurements of 3000 m running time, running time to exhaustion, and cardiorespiratory parameters during maximal exercise test and resting hematological status were performed before (Pre) and after 3 weeks of intermittent hypoxic exposure (Post). These measurements were repeated after the cessation of intermittent hypoxia for 3 weeks (Re). In the control group, the same parameters were determined at Pre, Post, and Re for the subjects not exposed to intermittent hypoxia. The athletes in both groups continued their normal training together at sea level throughout the experiment. In the hypoxic group, the 3000 m running time and running time to exhaustion during maximal exercise test improved. Neither cardiorespiratory parameters to maximal exercise nor resting hematological parameters were changed in either group at Post, whereas oxygen uptake (.V(O2)) during submaximal exercise decreased significantly in the hypoxic group. After cessation of intermittent hypoxia for 3 weeks, the improved 3000 m running time and running time to exhaustion tended to decline, and the decreased .V(O2) during submaximal exercise returned to Pre level. These results suggest that intermittent hypoxia at rest could improve endurance performance and submaximal exercise efficiency at sea level in trained endurance athletes, but these improvements are not maintained after the cessation of intermittent hypoxia for 3 weeks.     

Specific inspiratory muscle training in well-trained endurance athletes

PURPOSE: It has been reported that arterial O2 desaturation occurs during maximal aerobic exercise in elite endurance athletes and that it might be associated with respiratory muscle fatigue and relative hypoventilation. We hypothesized that specific inspiratory muscle training (SIMT) will result in improvement in respiratory muscle function and thereupon in aerobic capacity in well-trained endurance athletes. METHODS: Twenty well-trained endurance athletes volunteered to the study and were randomized into two groups: 10 athletes comprised the training group and received SIMT, and 10 athletes were assigned to a control group and received sham training. Inspiratory training was performed using a threshold inspiratory muscle trainer, for 0.5 h x d(-1) six times a week for 10 wk. Subjects in the control group received sham training with the same device, but with no resistance. RESULTS: Inspiratory muscle strength (PImax) increased significantly from 142.2 +/- 24.8 to 177.2 +/- 32.9 cm H2O (P < 0.005) in the training but remained unchanged in the control group. Inspiratory muscle endurance (PmPeak) also increased significantly, from 121.6 +/- 13.7 to 154.4 +/- 22.1 cm H2O (P < 0.005), in the training group, but not in the control group. The improvement in the inspiratory muscle performance in the training group was not associated with improvement in peak VEmax, VO2max breathing reserve (BR). or arterial O2 saturation (%SaO2), measured during or at the peak of the exercise test. CONCLUSIONS: It may be concluded that 10 wk of SIMT can increase the inspiratory muscle performance in well-trained athletes. However, this increase was not associated with improvement in aerobic capacity, as determined by VO2max, or in arterial O2 desaturation during maximal graded exercise challenge. The significance of such results is uncertain and further studies are needed to elucidate the role of respiratory muscle training in the improvement of aerobic-type exercise capacity.     

Effect of suspending exercise training on resting metabolic rate in women.

We tested the hypothesis that enhanced resting metabolic rate (RMR) in highly trained endurance athletes is an acute effect of prior exercise induced by catecholamines and not serum thyroxine. RMR and energy-regulating hormones were studied in nine highly trained women runners during habitual training (period I), and suspension of training (period II). Data were collected during the follicular phase of two consecutive menstrual cycles, confirmed by serum progesterone and estradiol. Subjects maintained training between the two periods. Total energy intake and diet composition, body weight, and oral temperature did not change from period I to period II (P greater than 0.05). With suspension of training, urinary epinephrine and nonrepinephrine excretion dropped (P less than 0.022) while serum TSH rose (P = 0.011) and free T4 did not change (P = 0.182). RMR (mean +/- SEM) was 274 +/- 6.2 and 252 +/- 7.8 kJ.h-1 for periods I and II, respectively, with repeated measures ANOVA indicating a drop in RMR occurred with cessation of exercise (P = 0.048). The augmentation of RMR by exercise lasted more than 15 h but less than 39 h post-exercise. The results suggest that the drop in catecholamines may partly explain the lower RMR following suspension of training.     

Impact of reduced training on performance in endurance athletes.

Many endurance athletes and coaches fear a decrement in physical conditioning and performance if training is reduced for several days or longer. This is largely unfounded. Maximal exercise measures (VO2max, maximal heart rate, maximal speed or workload) are maintained for 10 to 28 days with reductions in weekly training volume of up to 70 to 80%. Blood measures (creatine kinase, haemoglobin, haematocrit, blood volume) change positively or are maintained with 5 to 21 days of reduced training, as are glycogen storage and muscle oxidative capacities. Submaximal or improved with a 70 to 90% reduction in weekly volume over 6 to 21 days, provided that or improved with a 70 to 90% reduction in weekly volume over 6 to 21 days, provided that exercise frequency is reduced by no more than 20%. Athletic performance is improved or maintained with a 60 to 90% reduction in weekly training volume during a 6 to 21 day reduced training period, primarily due to an enhanced ability to exert muscular power. These findings suggest that endurance athletes should not refrain from reduced training prior to competition in an effort to improve performance, or for recovery from periods of intense training, injury, or staleness.     

Resting echocardiographic parameters after cessation of regular endurance training

Resting echocardiograms were examined in nonathletic healthy young men (controls, n = 16), in highly trained endurance athletes (n = 20), and in endurance athletes who stopped regular training (n = 40). The relative muscular wall thickness (Rel. MWTd), left ventricular internal diameters both in diastole and in systole (LVIDd, LVIDs), thus also the end-diastolic and end-systolic volumes (LVEDV, LVESV), and the stroke volume index (SVI) were greater in the endurance athletes still in training than in the nonathletes. The ejection fraction (EF), heart rate (HR), cardiac index (CI), and mean circumferential shortening velocity (Vcf) were significantly lower in the athletes. During the 60 days of detraining no change was seen in the Rel. MWTd, LVEDV, LVESV, and HR. The SVI became even greater; EF and Vcf rose up to the control level while CI exceeded it. The cardiovascular regulation is therefore assumed to undergo a peculiar shift during detraining in that a persisting cardiac enlargement and bradycardia is associated with a temporarily unstable autonomous control. This imbalance often leads to a hyperkinesis-like syndrome when an athlete stops endurance training abruptly.     

Echocardiographic findings in strength- and endurance-trained athletes.

Assessment of echocardiographic measurements in athletes should take into account the specific sport and the quantity and quality of training. In addition, values corrected for body dimensions, especially the active body mass, should be used rather than absolute values. All parts of the athlete's heart are enlarged and its performance increases. Highly trained endurance athletes show the most enlarged hearts. Athlete's heart can be observed in athletes of all ages including the young. However, it is rarer than generally assumed. To differentiate between physiological and pathological myocardial changes, the relationship between heart size and ergometric performance as well as the echocardiographically measured ratio between left ventricular (LV) myocardial thickness and volume are useful; the latter remains unchanged, on the whole, in endurance- and strength-trained athletes. Concentric hypertrophy cannot be induced by strength training alone; additional factors, such as hypertension, aortic stenosis, cardiomyopathy or anabolic steroid use can play an important role. When corrected for body dimensions, non-endurance-trained, e.g. strength-trained, athletes have standard heart sizes even if considerable time is devoted to training. Findings in healthy untrained persons with large body dimensions also indicate no significant difference between the increase of echocardiographic measures caused by training and that caused by growth. An LV myocardial thickness of 13mm is seldom exceeded even in the highly endurance-trained or anabolic drug-free strength trained athletes under physiological conditions. However, the echocardiographic differentiation of cardiomyopathy can be difficult if an individual is highly trained and has large body dimensions. In such cases, LV end-diastolic diameter may be up to 66 to 70mm. The upper normal value of LV muscle mass is 170 g/m2 for a physiological heart enlargement. Future areas of investigation should include: adaptative changes; of the right ventricle; differences in the regression of the athlete's heart after cessation of training; the differentiation between echocardiographic changes; in highly endurance-trained or combined strength-endurance-trained persons and pathological changes; the importance of heart size and endurance sports performance; and finally the influence of genetic factors.     

Effects of hydraulic circuit training following coronary artery bypass surgery

The effect of hydraulic circuit training (HCT) on stroke volume (SV), cardiac output (Qc), aerobic power (peak VO2), and muscular strength and endurance was evaluated in 24 post-coronary artery bypass (CABS) patients (mean age = 52.8 +/- 2.6 yr). All assessments other than muscular strength and endurance were based upon a symptom limited graded exercise test on a bicycle ergometer. Muscular strength and endurance were assessed on a Cybex II isokinetic dynamometer. Sixteen patients were assigned randomly to 8 wk of cycle training or HCT (N = 8 in each). Subjects assigned to cycle training exercised on bicycle ergometers. The HCT group exercised on a three-station circuit, completing three circuits per day. Each circuit consisted of three 20 s work intervals at each station with a 1:1 work:rest ratio. Results from the training groups were compared with results from eight patients who served as a nonexercising control group. Following training the peak VO2 was significantly increased in the training groups (20% and 11% for the cycle and HCT groups, respectively; P less than 0.05). For both training groups, the increase in peak VO2 was associated with increases in SV and Qc and a reduction in heart rate (HR) at submaximal levels of exercise (P less than 0.05). Only the HCT group demonstrated an increase in both muscular strength and endurance during knee and shoulder exercises (P less than 0.05). These findings suggest that a program of HCT can elicit improvements in cardiovascular fitness and muscular strength and endurance in post-CABS patients.     

The effect of differential training on isokinetic muscular endurance during acute thermally induced hypohydration

The purpose of this study was to test the effect of acute thermal hypohydration on the muscle endurance performance of three groups of differentially trained subjects. Group I consisted of six anaerobically trained athletes, Group II consisted of five aerobically trained athletes, and Group III consisted of six sedentary individuals. Experimental trials involved maximal leg extensions performed on a Cybex II dynamometer under conditions of euhydration and hypohydration of minus 3% body weight. Integrated electromyographic data were also collected during each trial to factor out motivation as a variable. The maximum number of leg extension repetitions performed at or above 50% of each subject's peak torque output were compared between treatments and among the three groups. A 2 x 3 factorial analysis of variance (ANOVA) showed a significant decrease in muscle endurance when comparing euhydration to hypohydration among the anaerobically trained subjects as well as among the sedentary subjects (P less than 0.05). The aerobically trained subjects showed no significant decline in muscle endurance when comparing performance under both experimental conditions. It was hypothesized that the training adaptations that occur with aerobic conditioning and are primarily associated with increased plasma volume may be the key to explaining these results.     

Adaptations to swimming training: influence of training volume

In an effort to assess the contributions of a period of increased training volume on swimming performance, two matched groups of collegiate male swimmers were studied before and during 25 wk of training. For the first 4 wk of this study, the two groups trained together in one session per day for approximately 1.5 h.d-1. During the following 6 wk (weeks 5-11), one group (LONG) trained two sessions per day, 1.5 h in the morning and 1.5 h in the afternoon. The other group (SHORT) continued to train once each day, in the afternoon with the LONG group. Over the final 14 wk of the study, both groups trained together in one session per day (1.5 h.d-1). Although the swimmers experienced significant improvements in swimming power, endurance, and performance throughout the 25 wk study, there were no differences between the groups. However, during the 6 wk period of increased training, the LONG group experienced a decline in sprinting velocity, whereas the SHORT group showed a significant increase in sprinting performance. The test results suggest that a 6 wk period of two 1.5 h training sessions per day does not enhance performance above that experienced with a single training session of 1.5 h each day. It was also noted that both groups showed little change in swimming endurance and power after the first 8 wk of training, though their performances improved significantly after each taper period.     

Évolution des coordinations musculaires au cours du pédalage chez le sujet âgé régulièrement entraîné en endurance

AimMuscular activity of elderly people regularly trained in endurance was recorded and compared to young adults to study the age-related effect on muscular coordination during cycling.MethodSixteen elderly people (seniors: 66,1 ± 5,8 years) and 10 young adults (juniors: 25,4 ± 4,6 years) with the same endurance training level, performed a 10 min cycling exercise at high power output. Before exercise, voluntary maximal isometric force (FMV) of knee extensors was assessed and compared between the two groups. During cycling, electromyographic activity of the main muscles involved in cycling was recorded with surface electrodes.Results and discussionResults indicate lower values of FMV for seniors than for juniors. During the cycling exercise, seniors are characterized by a lower agonistic muscle's activity and a higher antagonistic activity, when compared with juniors.ConclusionOur study confirms the decrease of force with ageing, even for elderly people regularly trained in endurance. Moreover the two groups of people seem to develop different muscular activation strategies. Endurance training with ageing could thus result in particular muscular activity in cycling.